Thanks to "Sinnerboy" on the greenbuilding forum for posing this. Will be of interest to some here..

http://arbota.com/insulation-test-ruling-hits-multi-foil-producers-23765/

Quote:

Written by Technology-observer
June 22nd, 2009 at 3:51 pm

Insulation test ruling hits multi-foil producers

Communities department rejects move from hot box testing to in-situ performance assessment

Multifoil manufacturers have been dealt a blow following the announcement from the Department for Communities and Local Government that there’s not enough evidence to support the use of in-situ performance testing for multi-foil insulation products.

Currently hot box testing is the accepted international standard for testing insulation materials. However, in 2007 Actis, which makes thermo-reflective insulation products, obtained a ruling from the High Court after it complained that the communities department had failed to consult properly over a testing method that discriminated against its multi-foil insulation product.

Following the consultation on the proposals for amending Part L of the Building Regulations, the department commissioned a review of the test methods for determining the thermal performance of building materials.

It has concluded that there was “no new substantive evidence on the robustness, exactness and repeatability to support the move from hot box characteristics to in-situ performances testing”.

In practice it means that to comply with the building regs you may have to continue to use multifoil in conjunction with conventional insulation and/or air gaps...or wait for them to produce a thicker/better multifoil that passes the hot box test.

I believe at least one manufacturer has got their product through the hot box text by using air gaps either side. However since the main selling point of multifoil is it's reduced thickness having to use additonal insulation or air gaps negates their claimed advantage.

It's been a long running saga involving the Advertising Standards people and the Building Research Establishment. For more read this..

http://www.foam-insulation.co.uk/insulation/multi-foil-insulation.htm

Personally I wouldn't rely on multifoil until the BRE agree the makers claimed U-Values.

CWatters wrote on Jun 24^th, 2009, 6:26pm:


But there's the fallacy. Thinner, I mean.  You have to allow for room for the foil to expand into the space between the rafters (and if you;re strictly adhering to the 50mm airgap there then it means you have to space out the multi-foil from the rafter.  Then you have to allow space for it expand in the other direction into the room. So you save ..what..5mm?? over normal kingspan.  Mind you, bloody sight easier to fit.

All these expensive reports!!

There are 7 houses that have been built nearby, foil insulation to the roof. There is never any frost on the roof and the houses are freezing cold in the winter. It doesn't take a rocket scientist or years of tests to work out it's ineffective.